TIME-RESOLVED LUMINESCENCE TECHNIQUE AS A PROBE FOR PHASE-TRANSITIONS IN SOME POLYSILOXANE LIQUID-CRYSTALS BEARING THE CHROMOPHORE 2,7-DIMETHOXY-N-METHYL CARBAZOLE (DMNMC) AS A PENDANT GROUP

Solid films of poly(methylsiloxanes) with side chains containing 2,7-dimethoxy-N-methyl-carbazole (DMNMC) pendant groups attached through aliphatic spacers (CH2)m where m = 3, 5 and 6 were studied photophysically. Time-correlated single-photon-counting measurements were performed on these films at temperatures encompassing the various mesophases obtained by differential thermal analysis (DTA). The decays are multiexponential in all cases. No rise time of excimer emission was observed such that the analysis was based on a three exponential decay. These decays have been attributed tntavively to quenched monomer-like emission, to dimers possibly made of antiparallel sandwich configurations and to ground state preformed excimer type-II emission. The fluorescence intensity fraction of the latter was shown to be the most sensitive to any mesophases in these polymer films. The smectic and nematic mesophases of polymer C5 have been detected. It is shown that the length of the spacer is playing a major role in the appearance of the mesogenic properties in these polymers.